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Subject: Re: Jump Label initialization
From: Jan Glauber <jang@linux.vnet.ibm.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Jason Baron <jbaron@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        "David S. Miller" <davem@davemloft.net>
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Date: Thu, 29 Sep 2011 14:04:54 +0200
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On Wed, 2011-09-28 at 19:14 -0700, Jeremy Fitzhardinge wrote:
> Hi all,
> 
> I'm trying to use the jump label machinery as part of the pv ticketlock
> work I'm doing on x86.
> 
> The problem I'm having at the moment is that I do my spinlock setup in
> smp_prepare_boot_cpu(), which happens before jump_label_init() gets
> called, and so the latter goes and nops out all my enabled jump label key.
> 
> I'm experimenting at the moment with a patch to allow
> jump_label_enable() to be called fairly early, and have that be
> respected by jump_label_init().  I'm doing this by replacing
> arch_jump_label_poke_text_early() with
> arch_jump_label_transform_early(), which shares most of its code with
> its non-early variant, except that it expects to run in a pre-SMP
> environment.
> 
> Does this seem plausible? (I haven't tested it yet.)
> 
> The x86, mips and sparc patches are fairly simple; I forgot to look at
> powerpc, and I didn't fully investigate s390.

s390 does not have the early() variant since it didn't need it. On
pre-SMP we probably don't need stop_machine() so creating
arch_jump_label_transform_early() by leaving out stop_machine()
and patching the code directly should be fine.